Often in wireless communications, such as cellular or personal communication services (PCS), remote units are limited in power, such as may result from the use of battery operated hand-held radio units. Accordingly, although a centralized communication array, such as a base transceiver station (BTS) providing network communication to a plurality of remote units, may possess sufficient power resources to provide a desired signal level throughout a service area in a forward link, the remote units may not be capable of providing a reverse link signal which matches the power of the forward link. Similarly, prudent use of resources may suggest conserving energy by the remote units, thus dictating a reverse link signal which does not match the power of the forward link. Accordingly, the use of high gain antenna beams, such as those provided by a directional narrow beam system, is often very desirable. Moreover, in addition to increased gain, such narrow beams allow a receiver to isolate the signal of interest from sources of interference which are sourced outside of the narrow beam.
The use of narrow antenna beams provides increases in gain over that of a wider antenna beam, although such narrow beams, by definition, do not provide communication within as large of an area as the more broad antenna beam. Accordingly, multiple and/or steerable narrow antenna beams are often used in order to direct a beam to a portion of a larger service area which includes a remote unit desiring communication services. By selectively directing the narrow antenna beams used in the reverse link a high gain antenna beam may be utilized to provide communication with a remote unit. Where multiple communication channels are used, such narrow beams are useful in the reverse link, for example, to selectively couple only those antenna beams having a channel of interest appearing therein to the appropriate radio receivers.
However, narrow antenna beams may not always be preferred in providing desired communication services. For example, the use of narrow antenna beams by definition limits the area in which communications may be conducted and, therefore, it may be advantageous to provide a signal in a wider area so as to increase the area in which communications may be conducted.
The above described directional or steerable antenna beams are often produced by a linear planar array of antenna elements. The antenna beams are formed by exciting the antenna elements, often disposed in vertical columns, by a signal having a predetermined phase differential so as to produce a composite radiation pattern combined in free space to have a predefined shape and direction, wherein the fewer such antenna elements excited by the signals having the predetermined phase differential the more broad the beam resulting therefrom. In order to steer this composite beam, the phase differential between the antenna elements, or columns, is adjusted to affect the composite radiation pattern. A multiple beam antenna array may be created through the use of predetermined sets of phase differentials, where each set of phase differential defines a beam of the multiple beam antenna. There are a number of methods of beam steering using matrix type beam forming networks, such as a Butler matrix, or adaptive circuitry that can be made to adjust parameters, such as, for example, might be directed from a computer algorithm. This latter circuitry is the basis for adaptive arrays.
These planar arrays of antenna elements and their associated signal feed networks, although typically well suited for providing a particular antenna beam width for which they are designed, generally do not provide various beam widths. For example, a planar array adapted to provide multiple narrow antenna beams will have an number of elements and element placement, including inter-element spacing, optimized for producing these multiple narrow antenna beams, as well as a feed network adapted to provide the proper phase progression at these antenna elements. Accordingly, if a wider antenna beam is desired, such as may be produced by energizing a smaller number of the antenna elements, the antenna element placement and/or spacing may not result in a formed antenna beam of desired shape. For example, if a single antenna element column is to be excited to provide a wide antenna beam, this single antenna column as it is disposed in the multiple beam planar array may provide an antenna beam of less than a desired width and/or be ladened with high order side lobes, nulls, and the like. Moreover, as the antenna elements of such an array are optimized for a particular antenna beam width, energizing different subsets of the antenna elements or columns will result in inconsistent formation of the alternate width antenna beams.
Accordingly, where multiple channels are to be broadcast throughout a wide area, whether via a single wide beam antenna or contiguous narrow antenna beams, such signals must be combined for transmission within the beam(s) covering the area to be serviced. This is because if multiple narrow beams are used to provide the channels throughout a wider service area, each channel is combined in the narrow antenna beams covering a portion of the desired service area. Where a wider beam produced from a typical prior art multiple narrow beam antenna array is used to provide coverage of the desired service area, in order to avoid the multiple channels having different coverage areas due to the inconsistent formation of the alternate width antenna beams, multiple amplifiers are combined for energizing a common subset of antenna elements.
However, combiners, such as auto-tune, or cavity, combiners providing summing of high power signals for transmission are often very lossy, such as on the order of 4 to 5 dB. Therefore, although it might be desirable to provide forward link signals in a wide service area, since power in the forward link is often sufficient to give a desired signal level throughout such an increased portion of the service area, reasons such as the need for narrow antenna beams in the reverse link and signal loss due to combining such signals for transmission often discourage the use of such wide antenna beams.
Accordingly, a need exists in the art for an antenna system which allows for the provision of differing antenna beam widths in both the forward and reverse links. Moreover, a need exists in the art for such a system to provide multiple channels within desired service areas using the differing antenna beam widths efficiently and without introducing substantial signal loss.